Emulsions (emulsified products) are widely employed in various fields closely linked to daily life, such as pharmaceuticals, cosmetics, foods, inks, and paints. When water and oil are left standing without mixing, they form a single “liquid-liquid” boundary. When they are vigorously stirred, droplets of oil are dispersed in the water or droplets of water are dispersed in the oil, creating numerous “liquid-liquid” boundaries and forming an emulsion. Emulsions formed of water and oil can be either oil-in-water (O/W) type emulsions, in which oil droplets are dispersed in water, or water-in-oil (W/O) type emulsions, in which water droplets are dispersed in oil. Primary examples of O/W type emulsions are milk, mayonnaise, and cosmetic emulsions. Examples of W/O type emulsions are butter and margarine.
The main known emulsification methods are mechanical emulsification, phase-inversion emulsification, liquid phase emulsification, and D emulsification.